The present invention relates generally to tight-buffered optical fibers and optical cables that contain tight-buffered fibers. More particularly, the present invention relates to tight-buffered optical fibers that include strength members embedded in a buffer layer and cables containing them.
Optical fibers are now in widespread use as a communication media. Typically, as illustrated in cross section in FIG. 1, a conventional optical fiber 100 comprises light-transmissive portion 102 enclosed by at least one layer of polymer coating 104. Polymer coating 104 is usually made of an acrylate material. Light-transmissive portion 102 in optical fiber 100 may be either glass or a polymer. If the optical fiber is glass, optical fiber 100 most often has an overall diameter of about 0.25 mm. If it is polymer, optical fiber 100 most often has an overall diameter of about 0.5 mm.
Optical fibers are often surrounded by one or more protective sheaths to form a buffer. In FIG. 1, for example, optical fiber 100 is surrounded by a buffer layer 106 to form tight-buffered optical fiber 110. The buffer provides mechanical and environmental protection for the optical fiber and may provide necessary spacing between numerous fibers grouped together so that industry-standard connectors can be used. Unlike standard optical fibers, tight-buffered optical fibers generally have an outer diameter of 0.9 mm. The buffer layers are most often made of thermoplastic polymers such as PVC, Nylon, or the like.
The protective sheath in a tight-buffered optical fiber may include several layers. For instance, release layers within the buffer layers may help to improve the strippability of the buffer layers that surround the optical fiber. Some layers or materials selected for the buffer layers often have specialized properties, such as flame retardancy.
Various patents describe conventional tight-buffered optical fibers. For example, U.S. Pat. No. 5,181,268, which is hereby incorporated by reference, discloses a strippable tight-buffered optical fiber that includes an optical fiber, a first protective coating in contact with the cladding, an interfacial layer for easy strippability in contact with the first coating, and a buffer layer in contact with the interfacial layer.
U.S. Pat. No. 5,977,202 and U.S. Pat. No. 6,208,790, both of which are incorporated herein by reference, disclose alternative materials for the tight-buffer layers. The '202 patent teaches a radiation-curable composition for use as an optical fiber material or coating. The '790 patent teaches an ultraviolet light-curable polymer matrix, which is applied to the optical fibers and is substantially instantaneously cured in-place at ambient temperatures.
Cables using tight-buffered optical fibers are often reinforced with strengthening yarns, such as aramid or fiberglass yarns. The strengthening yarns are disposed longitudinally around the tight-buffer layers, and an overall jacket encloses the tight-buffer layers and the strengthening yarns. For instance, FIG. 2 illustrates a cross-section of a simplex cable that contains a tight-buffered optical fiber. The tight-buffered optical fiber is reinforced by surrounding buffer layer 106 with a plurality of strength members 202 and enclosing the plurality of strength members 202 with an overall jacket 204. The strengthening yarns adds to the overall cable diameter.
U.S. Pat. No. 5,982,967 and U.S. Pat. No. 5,011,260, which are incorporated herein by reference, disclose tight-buffered optical fibers that include strengthening yarns. The '967 patent discloses a glass optical fiber surrounded by a nylon buffer layer. The buffer layer is surrounded by a plurality of aramid fiber strength members that are enclosed in an overall jacket. The '260 patent discloses a tight-buffered optical fiber comprising a glass core and cladding enclosed by at least one layer of coating material. The at least one coating material layer is in turn enclosed by a plastic buffer layer. The '260 patent also discloses a release layer intermediate the plastic buffer layer and the at least one layer of coating material. When incorporated into a cable, the tight-buffered optical fibers of the '260 patent are enclosed in an overall jacket with strengthening yarns disposed between the tight-buffered optical fiber and the jacket.
U.S. Pat. No. 4,893,893, which is incorporated herein by reference, discloses tight-buffered optical fibers that include a plurality of fibrous strands interposed between the optical fiber and an outer plastic buffer layer. The fibrous strands act as strength members for the buffered optical fiber. According to the '893 patent, the buffer layer is tubed over the strands with a controlled drawdown instead of being applied by pressure extrusion. Consequently, the buffer layer is disposed concentrically about the strength members and has a predetermined compressive engagement therewith, which allows for controlled stripability of the buffer layer from the fiber.
The '893 patent also discloses a duplex optical fiber cable, which includes two tight-buffered optical fibers of the above construction. The two tight-buffered optical fibers are enclosed in a common outer jacket with a rip cord positioned between the two tight-buffered optical fibers. The rip cord is used to tear a slit in the jacket, which allows for the removal of the jacket from the two buffered optical fibers.
Applicants have observed that existing cables using tight-buffered optical fibers do not use strength members effectively or efficiently. For instance, these types of tight-buffered fibers have strength members that are separated from the optical fiber by at least a layer of polymer coating. Moreover, by containing strength members between buffer layers, conventional tight-buffered optical fibers sacrifice thickness in the remaining protective layers. Consequently, the conventional tight-buffered optical fiber does not receive the maximum amount of protection from the environment.